Polyurethanes prepared from polyols containing cyanoalkyl ether groups

ABSTRACT

This invention relates to elastomeric and rigid urethane polymers and prepolymers which have been prepared from polyols containing cyanoalkyl ether groups.

ilnited States atent Cantor et a].

I 3,903,054 Sept. 2, 1975 POLYURETHANES PREPARED FROM POLYOLS CONTAINING CYANOALKYL ETHER GROUPS Stephen E. Cantor; Thomas J. Brett, Jr., both of Cheshire, Conn.

Assignee: Uniroyal, Inc., New York, NY.

Filed: Feb. 25, 1974 Appl. No.: 445,729

Related US. Application Data Division of Ser. No. 227,647, Feb. 18, 1972, Pat. No. 3,816,425.

Inventors:

US. Cl. 260/775 AQ; 260/25 AQ Int. Cl C08g 22/16 Field of Search 260/775 AQ References Cited UNITED STATES PATENTS Bedoit 260/858 Currier et a1. 260/77.5 AQ Tucker 260/823 Cantor 260/8073 Cantor et a1. 260/775 AQ Primary Examiner-M. J. Welsh Attorney, Agent, or Firm-Willard R. Sprowls, Esq.

ABSTRACT groups.

4 Claims, No Drawings POLYURETHANES PREPARED FROM POLYOLS CONTAINING CYANOALKYL ETHER GROUPS This is a division of application Ser. No. 227,647, filed Feb. 18, 1972, which became US. Pat. No. 3,816,425 on June 11, 1974.

Urethane polymers can have many special characteristics such as resistance to shock, oxidation, fuels and oils, depending upon the type of polymeric polyolpolyether or polyester used in their preparation. Polyester-polyol polyurethanes resist dry-cleaning solvents such as trichloroethylene and carbon tetrachloride, but are susceptible to hydrolysis from bases encountered in detergent washings. Polyether-polyol polyurethanes have the opposite characteristics, having superior hydrolytic stability, especially at high temperatures. The polyurethanes made from the polyether polyols of this invention are resistant both to hydrolysis and to attack by non-polar fluids and, particularly, to dry-cleaning solvents.

The polyols of this invention contain from about 1 to about percent, preferably from about 5.5 to about 15 percent, and, most preferably, from about 7 to about 12% cyano groups by weight, based on the weight of the polyol. They typically have a hydroxyl number from about to about 600, and, preferably, from about 50 to about 500, but they may have hydroxyl numbers outside these ranges. Their molecular weight is typically from about 250 to about 4500, but is preferably from 450 to about 2300. These polyols contain one or more moieties selected from those having the formula (1):

wherein R and R are the same or different, and are selected from hydrogen and alkyl groups containing one to four carbon atoms; R is hydrogen or an alkyl group containing one to three carbon atoms; X and Y are the same or different, and are selected from the group consisting of hydrogen, fluorine, chlorine, bromine and iodine; n is an integer in the range 1 to 3; and Q has a valence of n plus 1, and is an alkyl group containing 1 to 4 carbon atoms, a cycloalkyl group containing five or six carbon atoms, or phenyl. The moieties of formula (1) in any particular polyol may all be the same, or there may be two or more different kinds of moieties in each, provided that the total hydroxyl number, the total percentage of cyano-nitrogen groups, and the molecular weight of the particular polyol are all within the specified ranges.

The moieties of formula (I) are derived from such compounds as cyanoalkyland halocyanoalkyl epoxy ethers. These epoxides are described in copending US. Pat. application Ser. No. 227,648, filed on the same day as this case, which became US. Pat. No. 3,799,895 on Mar. 26, 1974, and in US. Pat. No. 3,410,810, issued Nov. 12, 1968, the disclosures of which are incorporated herein by reference. Briefly, the epoxides of 227,648 are compounds of the formula (11):

wherein R and R are the same or different, and are hydrogen or an alkyl group of l to 4 carbon atoms; R is hydrogen or an alkyl group of 1 to 3 carbon atoms; Q has a valence of 11 plus 1, and is an alkyl group of l to 4 carbon atoms, a cycloalkyl group of 5 or 6 carbon atoms, or phenyl; X is halogen such as fluorine, chlorine, bromine or iodine; and n is an integer of l to 3.

The polyols may also contain the residue of one or more polyfunctional initiators. These are active-hydrogen-containing compounds which may be monomeric or even higher molecular weight compounds made from more than one kind of active-hydrogencontaining compound. Preferably, the initiator contains from 2 to 8 active sites to which the epoxides described above can add, and is a mono-, di-, trior higher aromatic, aliphatic or heterocyclic polyamine, an alcohol such as an aliphatic polyol, or a mixture of two or more of these initiators.

Examples of such initiators are: ethylene glycol, propylene glycol, glycerine, trimethylolpropane, pentaerythritol, arabitol, sorbitol, maltose, sucrose, ammonia, diethanolamine, triethanolamine, dipropanolamine, tripropanolamine, diethanolpropanolamine. tributanolamine, 2 ,4-toluene diaminc 4,4 diphcnylmethane diamine, p,p,p"-triphenylmethanetriamine, ethylene-di-amine, propylenediamine, propylenctriamine, N,N,N ',N '-tctral is-( 2- hydroxypropyl) ethylenediamine, diethylenetriamine, p-amino aniline, 1,5-diamino naphthalene, 2,4-diamino toluene, ethylene diamine, 2,6-diamino pyridine, N-aminoalkylpiperazines and the like. Though not preferred, it is also possible to use aliphatic thiols such as alkyl thiols.

The polyols of this invention may also optionally contain residues of one or more alkylene, arylene, or aralkylene oxides, tetrahydrofuran, or halogenated derivatives of any of these compounds. Any particular polyol of the invention may contain two or more different kinds of such residues provided that the hydroxyl number, cyano-nitrogen content, and molecular weight of the polyol are in the abovedescribed ranges. See US. Pat. No. 3,410,810, columns 2 and 3, for a detailed description of some of these compounds.

Examples of these co-monomers are: tetrohydrofuran, epichlorohydrin, epibromohydrin, ethylene oxide, propylene oxide, butene oxide, isobutylene oxide, vinylchloride epoxide, methallyl chloride epoxide, dichloroisobutylene epoxide, styrene oxide, alphamethyl-styreneoxide, divinylbenzene monoxide, isopropyl glycidyl ether, chlorophenyl glycidyl ether, ethyl glycidyl ether, allylglycidyl ether, isopropenyl glycidyl ether, and the like.

The polyols of the invention can be made by reacting one or more cyanoalkyl epoxy ethers or halocyanoepoxy ethers, or both, with a polyfunctional initiator such as ethylene glycol, and, optionally, with tetrahydrofuran, one or more alkylene, arylene, or aralkylene oxides, or some combination thereof in the presence of a Lewis acid catalyst such as boron trifluoride etherate as taught by Murback etal. in lnd. Eng. Chem. Vol. 52 No. 9 p. 772 (1960). The reaction is typically conducted at temperatures in the range of minus 20 to 20 degrees Centigrade (C), at pressures in the range of 1 to 2 atmospheres, and, conveniently, in an inert, nonpolar organic solvent such as methylene dichloride.

In practice, the reactants are mixed in any desired order in a common solvent, a solution containing the catalyst is added, and the resulting mixture is stirred for a time period in the range of 4 to 30 hours, usually to 20 hours. The catalyst is deactivated, and the polyol is recovered by solvent extraction or some other convenient method.

The polyols of the invention have many uses, but an important use is in the manufacture of polyurethane polymers and prepolymers. The polyurethane polymers are made in either a one-stage process, which directly produces the elastomeric or rigid polyurethane of the invention, or in a two-stage process, in which first the urethane prepolymers of the invention are formed and, from them, the polyurethane polymers of the invention. Generally, higher molecular weight polyols of this invention are preferred for making the elastomeric polyurethanes; lower molecular weight polyols are preferred for making more rigid polyurethane polymers. The higher the functionality of the polyol of the invention, the greater the probability of forming a rigid polyurethane. As examples 34 and 35 show, the polyurethanes of the invention can be made from mixtures of two or more different polyols, and the mixture may include different polyols within, and outside of, those of this invention. Examples of such polyols are the propoxylatcd N-aminoethylpiperazines described in U.S. Pat. No. 3,251,788 and U.S. Pat. No. 3,251,787.

1n the one stage process, one or more of the new polyols are reacted with one or more organic polyisocyanates. The amount of polyisocyanate used is approximately stoichiometrically equivalent to the number of active hydrogens atoms in the polyol. Although an amount of polyisocyanate at least stoichiometrically equivalent to the reactive hydrogen atoms of the polyol should be used for best results, an excess of up to about 2.5 isocyanate groups per reactive hydrogen atom, or even more, can be used.

In the two-stage process, one or more of the new polyols is reacted with one or more organic polyisocyanates in an amount that exceeds the stoichiometric equivalent of the reactive hydrogen atoms in the polyol to obtain a prepolymer having many free, unreacted isocyanate groups. The excess will typically be sufficient to produce at least 3%, and preferably 5 to 7%, by weight, of free isocyanate groups in the prepolymer.

The prepolymer is preferably prepared in a moisturefree atmosphere to prevent premature curing. Typically, the reaction is effected under a nitrogen blanket at a temperature in the range 60 to 100C. The prepolymer can be prepared in a solvent if desired. Suitable solvents include: monoethylether acetate, xylene, toluene, methylethylketone, methylisobutylketone, cyclohexanone and other alkyl-substitutcd ketones and acetates, either alone or mixed with each other.

The new prepolymers are converted to polyurethanetype polymers of the invention by curing the prepolymers under atmospheric conditions, where the free isocyanate groups react with the moisture in the air to effect solidification by cross-linking. The curing atmosphere should contain at least relative humidity, and preferably from about 35 to about 65% relative humidity. The temperature of the atmosphere may range from room temperature of about 20C. to 60C. 1f de sired, however, the prepolymer can be cured more rapidly at a temperature in the range of 60 to 200C.

Although the prepolymers cure satisfactorily without catalysts, it is possible to use catalysts such as dibutyl tin dilaurate, trimethylpiperazine, stannous octoate, triethylamine, 1,4-diazole bicyclo-[2,2,2]-octane, and the like, to accelerate the curing process.

The curing can also be effected by employing various chain extending agents in combination with the prepolymers of the invention. The chain extender is preferably employed in an amount that is stoichiometric with respect to the isocyanate-terminated prepolymer. Suitable chain extenders include low molecular weight diols such as butanel,4-diol, polypropylene diol, oxypropylated aniline, ethylene glycol, catechol oxypropylated ethylene diamine, polyoxypropylene diamine, 4,4'-methylene bis(o-chloroaniline), and mixtures thereof.

Among the organic polyisocyanates which can be used in either the one or two-stage processes of making the polyurethanes of the invention are cyclic and acyclic aliphatic polyisocyanates, heterocyclic polyisocyanates, and aromatic polyisocyanates. Best results are obtained with aromatic polyisocyanates, and they are preferred. Diisocyanates, most preferred, include compounds such as hexamethylene diisocyanate, cyclohexyl diisocyanate, 2,6-toluylene diisocyanate, 2,4- toluylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethanc diisocyanate, 1,5- naphthalene diisocyanate, lmethyl2,4-diisocyanate- 5-chlorobcnzene, 2,4-diisocyanatc-s-triazine, 1- methyl-Z,4-diisocyanatocyclohexene. p-phenylene diisocyanate, 1,4-naphthalene diisocyanate, 4,4',4"- triphenylmethanc triisocyanate, the urea diisocyanates, and the dimers, trimers and other polymers of po1yisocyanates, and the like.

If desired, the polyurethanes of the invention can be made into foams by incorporating a foaming agent in the urethane reactants causing the polyurethane to expand as it forms.

The following examples illustrate the preparation of the polyols of this invention, their conversion to polyurethane prepolymers and polymers, and the high resistance of the polyurethanes to both polar and nonpolar fluids.

EXAMPLES l to 12 Preparation of Polyols EXAMPLE 1 A 250-milliliter (ml), 3-necked flask, fitted with a stirrer, thermometer, and dropping funnel, was charged with 43 grams (0.6 mole) of pure, dry tetrohydrofuran, 6.1 grams (0.1 mole) of ethylene glycol, 52 grams (0.4 mole) cyanoethyl glycidyl ether and grams (1.7 mole) of 1,2-dichloroethane. The solution was cooled to a temperature in the range l0 to 5C. in an isopropanol/dry-icebath. Then 40 grams (0.98 mole) of ethylene oxide was added. Finally, 14 grams (0.1 mole) of boron trifluoride etherate catalyst diluted with 50 grams of 1,2-dich1oromethane was added slowly over a period of 1.5 hours while the temperature was maintained in the l0 to 5C. range. The reaction mixture was stirred for 19 hours while maintaining the temperature at about 3C., after which time 40 grams of a 10% ammonium hydroxide solution was added to neutralize the catalyst. The resulting cloudy solution was washed 3 times with 100 milliliter portions of sodium chloride and 1% sodium bicarbonate. The organic layer was collected and dried over anhydrous magnesium sul- EXAMPLE 13 Polyurethane Prepolymer Prepared From Polytetramcthylene Glycol (Comparative Example) phate and filtered in order to remove the drying agent. 5 into a 550 milliliter resin t fitted with 11 The solvent was removed from the organic layer by disthermometer and a stirrer, were placed 28 grams (0.16 tillation, and the remaining viscous oil was heated to mole) of tolylene-2.4-diisocyanate (TDI) and 100 160C millimeters g PrCSSurC) for 1 u I grams (g) (0.1 mole) ofa commercially available polymove any remaining eyanoethylglyeidyl ether monot th l glycol (Polymeg 1000 Quaker Oats mer. The polyol yield was 100 grams (70%) having 10 Co.) havinga molecular weight of 1000. These materi- Brookfield viscosity f 1 HI P ki r00m als were stirred at a temperature of 80C. for 4 hours Pcmturo under a nitrogen atmosphere resulting in 122 g of a The product had a negligible acid number, contained thick lightbrown urethane prcpolymcr having an 3' i 4 nitrogen y wugiiti hydroxyl i f of amine equlvalent of 1317 and an lsocyanato group eon- 822, and a molecular weight of 1350. The 3.89 nl tromm of 11217! by weight of the p p y gen indicated 35% incorporation of eyanoethylglycldyl ether in the polyol. EXAMPLES 14 to 32 A genes Polyols was prepared Slmllar fdshlon Prepolymers Prepared From the Polyols of Examples 1 from eomblnatlons of eyanoethylglyeidyl ether and varto 12 ious cyclic oxides. Results for examples 2 to 12 are Summarized in Table I. The polyols of examples 2 to 1 1 Several of the polyether polyols whose preparation are within this invention. The polyol of example 12. a and propcmes are described m examples 1 to 12 and comparative example, is not within the invention. Table i were Com/("Rad to Polyurethane P p y In Table 1, various abbreviations are used for simplieusing generally the Proccdure described examplc ity. Their meanings are: CEGE cyanoethylglyeidyl The results are summarized in Table 11. This table ethenJHF -tetrahydrofuran; PO Q propylene oxide; EO shows that the polyols of this invention are readily eonethylene oxide; ECH epichlorohydrin; EBH epiverted into prepolymers. for the prepolymer yield exbrornohydrin; ECD ethylene dichloride". BR, boron eeeded 90 percent by weight of the theoretical yield in trifluorideetherate; and EG ethylene glycol. each of the examples of the invention.

TABLE I Preparation of Polyether Polyols Example No. 2 3 4 S 6 8 10 1 l 11 Monomers 'CEGE. moles ".36 1.77 1.18 0.59 1.18 20 1.2 0.5 1.0 0.81 THF moles 1.04 2.08 2.08 1.04 1.8 (1.35 2.6 PO moles 1.29 1.29

EO moles 0.33 3.0 0.08 0.3 0.9 ECH moles 3.0

EBH moles ().7 Solvent Em. grams 930 7x0 7x0 7x0 7x0 l000 e00 200 600 1000 ca. 900 Catalyst RF... moles 0.2924 0.290 0.074 0.074 0.296 0.24 0.30 0.05 0.30 0.22 0018 E0 1110108 0.296 (1.296 0.074 0.074 0.296 0.22 0.30 0.05 0.30 0.22 l.00 Reaction Temp. C. l()-+l0 l5-+8 "IO-+11) 1()-+5 3 Reaction Period. hrs. ca. 12 I) 20 18 10 20 Yield. v 79 07 x2 7x 7x 65 x4 63 Polymer CEGE. '2; (Weight) I00 77 02.5 27.5 50 9e 35 9s 2s Hydroxyl No. 79 59 4| 65 131 82 150 83 TABLE 11 Polyurethane Prepolymer Preparation Example N0. l4 15 16 17 18 l9 20 2l 22 PoIyoHExamplc) (12) (1) (2) (3) (4) (5) Polyol. grams 83 83 89 199 121 163 100 73 TDl. grams 28 28 23 55 27.5 31 34 28 28 Reaction Temp. C. 83 83 80 80 80 80 80 83 83 Reaction Period. hrs. 3 4 4 4 4 4 4 3 3 Yield. grams 107 109 Amine Equivalent 626 609 1273 1480 l037 925 l072 835 831 6.55 6.85 3.30 2.84 4.06 4.54 3.82 5.03 5.07

lsocyanatc Content. 7! (Weight EXAMPLES 23 to 32 Preparation of Cured Polyurethanes From the Prepolymers of Examples 13 to 22 Each of the prepolymers of. examples-13 to 22 were converted to cured elastomeric polyurethanes using the following general procedure: i

Procedure Each prepolymer was heated to a temperature of about 100C. in an open, 250m1 beaker. A polyamine was heated in a separate beaker until it melted. The hot, molten poly'amine was poured into the beaker containing the hot prepolymer. and the resulting mixture was stirred vigorously for 30 seconds. The mixture was poured into a mold preheated to about 50C., and the mold was subjected to a pressure of about 200 atmospheres to effect cure. Curing time and temperature, and the properties of each polyurethane produced, 'are summarized in Table 111.

The amount of polyamine about 90 percent of the amine equivalent of the prepolymer was calculated from the following equation: I

wherein PA means polyaminc; PP, prepolymer; PK, molecular weight of the polyamine; F, the functionality of the polyamine, and AE. the amine equivalent of the prepolymer.

In Table 111. the abbreviations CEGE, PO and E have the meanings given above in connection with Table l. PTMG means poly(tetramethylene glycol); TCE, triehloroethylene. Fuel B is a mixture of isooctane (70% by weight) and toluene (30% by weight).

urethanes of this inverition'(examples -32) over the prior art polyurethanes of examples 23 and 24, even where the nitrile content is low as 5.6% by weight (example 28). Most remarkable is the high resistance to swelling in Fuel B. even with polyurethane elastomers having low crosslinkdensities, withour substantial loss of the high water resistance such polyurethanes typically have. t

' EXAMPLE 33 Preparation of N,N";N"-tris[2-hydroxy-3-(betacyanoethoxy )propyl l-N '-arninoethylpiperazine Into a 1' liter, three-neckedround-bottomed flask, equipped with a stirrer, a thermometer, a dropping funnel and inlet and outlet tubes for dry nitrogen were placed 42.2 grams (0.33 mole) of N-aminoethylpiperazine. This compound, a liquid, was heated with an oil bath to about 70C. while a stream of dry nitrogen was passed continuously over the heated liquid. Then 127 grams 1 mole of CEGE was added incrementally over a period of 2% hours while the reaction mixture was maintained .at a temperature of 75 to 88C.

After all the CEGE was added, the mixture was maintained at a temperature of 83C. for 2 hours, after which time 155 g of product, a clear, reddish, viscous material was isolated. The product was soluble in water and acetone, had a hydroxyl number of 397.7, and showed absorptions of 3500 and 2240 cm upon infrared analysis. These values are characteristic of hydroxyl and cyano groups.

The polyol prepared in this example was used to prepare the new flexible and rigid polyurethane foams of TABLE lll Preparation of Cured Polyurethanes Example No. 2 24 25 26 28 29 31 32 Polyether Polyol (Example) (l2) (2) (3) 4) (5) (6) (7) (1) (8) Composition. "/1 Weight CEGE 100 77 62.5 28 50 96 35 PTMG 100. 82.5 23 37.5 36* 25* 65 PO 36* 25* E0 17.5 4

Hydroxyl number 12 83 79 90 59 41 64 I31 82 82 Polyurethane Prepolymer (Example) (l3) (14) (16) (17) (18) (19) (20) (2|) (15) (22) Amine equivalent 1317 626 1273 1480 1037 925 1072 835 609 831 Polyurethane Preparation Prcpolymer, grams 40 60 60 60 60 60 60 40 60 MOCA. grams 3.8 7.6 5.6 4.9 6.9 7.8 6.7 5.8 6.8 5.8

Cure Temp. C l(l4 lUO I04 I04 I04 104 l()4 100 N14 l()4 Cure Period. minutes 60 60 60 60 60 60 50 60 Post-cure Temp. C 49 4) 49 70 Post-cure Period. hrs. 24 24 24 24 24 Polyurethane. Physical Properties 100% Modulus, psi 500 630 320 330 .650 320 310 1040 640 310 Tensile Strength, psi 2500 4|()(l 850 790 [I20 I010 910 [710 1230 1030 Elongation at Break, /z 600 460 260 420 320 540 420 150 300 420 Hardness, Shore A 66 67 84 74 6) H 84 70 Swell in Fuel B, '71 37.1 28 0.7 1.4 1.4 7.2 3.) 0.6 4.6 3.8"

Swell in TCE. 71 196 177 4.5 26.9 59 108 79 3.5 70 10 Swell in Water. '/1 1.1 3.9 (1.8 4.2 3.2 2.4 8.0 4.2 5.3 7.6

calculated The data in Table lll show the dramatic and unexpected improvement in solvent resistance of the polyexamples 34 and 35. Both new foams had excellent resistance to polar and non-polar solvents.

Example 34 Preparation of Flexible Polyurethane Foam A (Invention) Recipe B (Control) l) Polyol l. grams 2) Polyol ll grams 3) HCAP grams 1 4) Water grams 5) TMAP grams 6) Surfactant grams 7) PIC grams 8) Catalyst grams l) Ethoxy-cnppetl propoxylated glycerine. molecular weight 4700 2) Propoxylated N-aminoethylpiperavine 3) N.N" N "-trisl Z-hydroxy-J-t heta-cyanoethuxyl propyl l-N '-aminoethylpipurazine 5) Trimethylaminoethylpiperazine h) Dimethylsiloxane oil 7) Polyi' cyan-ate 1 70% tolylene tliisocyanate 30'! crude 4 4'diphenylmethane diisocym te K) Organotin catalyst Example 35 Preparation of Rigid Polyurethane Foam Recipe A (Invention) B (Control) I) Pulyol lll, grams 50 50 2) Polyol ll grams S 3) HCAP O 4) Surfactant grams L5 L5 5) Chelating Agent grams l.() l.()

6) Blowing Agent grams 12.0 12.0

7) Water grams 0.025 0.025 ll) Catalyst grams l.l5 L5 9) Polyisoeyanate grams l22. 107.

l (il werine initialed polyether polyol, molecular weight 400 2) As in example 34 3) As in example 34 4) ()rganosilicune 5) Acelylaeuione 6) Trichlorolluoromcthane 8) Dimethylethanolamine Crude 4.4'-diphenylme'thane diisocyanate The above ingredients, with the exception of the polyisocyanate, were thoroughly mixed in a beaker at room temperature and then (9) was added while stirring for about l5 seconds. After a few seconds the reaction started, leading in both cases to rigid polyurethane foams. The polymer A showed improved solvent resistance over polymer B.

We claim:

1. A polyurethane prepolymer obtained by reacting at least one organic polyisocyanate with at least one polyol. the polyisocyanate being present in an amount sufficient to provide from L2 to 2.2 isocyanato groups per active hydrogen site in the polyol, said polyol having a hydroxyl number of 40 to 400, having from 1 to 20% cyano groups by weight, based on the weight of the polyol, and having a group of the formula:

wherein R is hydrogen or methyl.

2. A polyurethane prepared by reacting at least one organic polyisocyanate with at least one polyol wherein the polyisocyanate is used in an amount at least stoiehiometrically equivalent to the active hydrogen groups in the polyol, said polyol having a hydroxyl number of 40 to 400, having from 1 to 20% cyano groups by weight, based on the weightof the polyol, and having a group of the formula:

wherein R is hydrogen or methyl.

3. The polyurethane of claim 1 prepared by reacting N,N ,N -tris[ 2-hydroxy-3-( beta-cyanoethoxy) propyll-N'-aminocthylpiperazine, ethoxy-capped propoxylated glycerine, 4,4'-diphenylmethane diisocyanate. and tolylene diisocyanate.

4. The polyurethane of claim 2 prepared by reacting glyccrine-initiated polyether polyol, N.N",N"-tris[2- hydroxy-3-(beta-cyanoethoxy) propyl]-N'-aminoethylpiperazine, water, and 4,4-diphenylrnethane diisocya- 

1. A polyurethane prepolymer obtained by reacting at least one organic polyisocyanate with at least one polyol, the polyisocyanate being present in an amount sufficient to provide from 1.2 to 2.2 isocyanato groups per active hydrogen site in the polyol, said polyol having a hydroxyl number of 40 to 400, having from 1 to 20% cyano groups by weight, based on the weight of the polyol, and having a group of the formula: -CH2-OCHR3-CH2-CN wherein R3 is hydrogen or methyl.
 2. A polyurethane prepared by reacting at least one organic polyisocyanate with at least one polyol wherein the polyisocyanate is used in an amount at least stoichiometrically equivalent to the active hydrogen groups in the polyol, said polyol having a hydroxyl number of 40 to 400, having from 1 to 20% cyano groups by weight, based on the weight of the polyol, and having a group of the formula: -CH2-OCHR3-CH2-CN wherein R3 is hydrogen or methyl.
 3. The polyurethane of claim 1 prepared by reacting N,N'''',N''''-tris(2-hydroxy-3-(beta-cyanoethoxy) propyl)-N''-aminoethylpiperazine, ethoxy-capped propoxylated glycerine, 4,4''-diphenylmethane diisocyanate, and tolylene diisocyanate.
 4. The polyurethane of claim 2 prepared by reacting glycerine-initiated polyether polyol, N,N'''',N''''-tris(2-hydroxy-3-(beta-cyanoethoxy) propyl)-N''-aminoethylpiperazine, water, and 4,4''-diphenylmethane diisocyanate. 